Polymerizable N-substituted amides, and more specifically N-olefinically unsaturated amidodialkyl acetals, are useful monomers for free radical polymerization, especially with comonomers such as ethylene, vinyl acetate, vinyl chloride, and the like. Such acrylamides which contain the dialkyl acetal group are able to introduce into polymers the capability of internal crosslinking without the side production of formaldehyde. These polymers have found utility in a number of areas including binders, adhesives and coatings. In this regard, the acetal functionality is particularly desirable.
U.S. Pat. Nos. 4,663,410 and 4,691,026, Pinschmidt et al., (1987) disclose the preparation of acrylamidobutyraldehyde dimethylacetal (ABDA) by the reaction of amines and acid chlorides in the presence of a base to remove the hydrogen chloride which is formed in the reaction. The utility of the acrylamides containing dimethylacetal groups is also demonstrated. These patents also suggest other methods for preparing the valuable monomer, such as by the addition of aminoacetal compounds to maleic anhydride in an inert solvent or by reacting an olefinically unsaturated carboxylic acid with an aminoacetal or ketal using dehydrating agents, such as SOCl.sub.2 or carbodiimides. One of the alternate routes suggested is the reaction of an alkylamine with alkyl acrylates to give acrylamides. This reaction, however, involves Michael addition of the amine to the double bond, which is reversible at higher temperatures allowing net formation of N-alkylacrylamides. It is further suggested that the Michael reaction can be suppressed by preforming reversible alcohol or alkylamine acrylate adducts. Such a procedure would be very attractive because it requires much less expensive feedstocks than the acryloyl chlorides of the principle method disclosed by these patents. The problem, however, has been consistently inadequate yields because of the inability to suppress or circumvent the Michael reaction.
In general, the reaction of alkylamines with acrylate esters has been known for decades. For example, U.S. Pat. No. 2,451,436 to Erickson (1948) discloses the reaction of n-butylamine with ethyl acrylate and the conversion of the N-alkyl-.beta.-alkylaminopropionamide by heating in the presence of an acid, for example sulfuric acid to split off the alkylamine salt which is formed as a part of the Michael reaction. This leaves N-alkyl-.alpha.,.beta.-unsaturated amide, such as N-n-butylacrylamide. Even though the best yields disclosed are only about 75%, the conditions and particularly the acidic conditions required would not be suitable for the reaction of amines containing acetal groups which are not stable under such acidic conditions.
U.S. Pat. No. 2,529,838 Erickson (1950), discloses making N,N-dialkylacrylamides by heating an acrylic ester with an dialkylamine, where the alkyl groups must contain five or more carbon atoms. The example, however, shows only about 10% yield.
U.S. Pat. No. 2,587,209 to Phillips et al., (1952), discloses that .beta.-(lower alkoxy)propionamides can be dealcoholated catalytically in the vapor phase to acrylamides. U.K Pat. No. 728,955 (1955) also discloses a vapor phase thermal disassociation of derivatives of propionamides, but neither of these references which describe vapor phase deblocking of the double bond of the acrylamide suggest application of the process to compounds which contain acetal groups.
U.S. Pat. No. 2,719,178 to Coover et al., (1955), discloses that N-alkyl-.beta.-N-alkylaminopropionamides can be converted to the corresponding unsaturated .alpha.,.beta.-unsaturated amides by pyrolysis of the vaporized feed at 300.degree. to 550.degree. C., using a suitable catalyst such as alumina silica, with or without a diluent. These conditions are far too extreme for acetals and could not be used with compounds which contain the dialkyl acetal groups such as those which have been described to be highly useful comonomers in the patents to Pinschmidt et al., cited above.
U.S. Pat. No. 3,878,247 to Moss et al, (1975) describes a noncatalytic process for preparing N-(tertiaryaminoalkyl)acrylamides. The process starts by reacting a tertiaryaminoalkyl amine with an acrylic acid or ester at about 100.degree. to 200.degree. C. to form a beta-aminopropionamide, which is then converted by heating at 180.degree. to 300.degree. C. to the N-(tertiaryaminoalkyl)acrylamide. Example II of this reference describes the cracking of the 3-dimethylaminopropylamine Michael adduct of N-(3-dimethylaminopropyl)acrylamide at 205.degree. to 275.degree. C. followed by distillation of the product mix of amine and amide to obtain the amide in 72% yield. To attempt such a reaction with a primary amine having dialkylacetal groups under such drastic cracking conditions, would give severe product decomposition. Also rapid back-reaction of the product acrylamide with coproduct primary amine makes the acrylamide isolation impossible with acceptable yields.
One possible route following the suggestion in the Pinschmidt et al., patents is to use a blocking technique to suppress the Michael reaction. This approach has been used as described in U.S. Pat. No. 3,914,303 to Daniher et al., (1975) which describes preparing N,N-dialkylamide of an .alpha.,.beta.-olefinically unsaturated monocarboxylic acid. The procedure requires the use of a polyol solvent-catalyst for the amidation reaction between the .beta.-ether-substituted monocarboxylic acid ester and the dialkyl amine. Glycerin is given as a preferred solvent-catalyst. It is stated that non-catalytic amidation at 100.degree. to 125.degree. C. resulted in byproduct formation of appreciable amounts of .beta.-methoxypropionic acid. Use of the polyol is said to minimize side reactions and increase yield. Pyrolysis, however, is used to convert the .beta.-ether-substituted amide to the unsaturated amide forming, for example, N,N-dimethyl .beta.-methoxypropionamide which is converted to N,N-dimethylacrylamide using an acid cracking catalyst. This technique would destroy an amide which contained dialkyl acetal groups.
More recently, attempts have been made to go directly to the N-substituted amide of acrylic or methacrylic acid by reacting an alkyl ester of acrylic or methacrylic acid with an amine. Such a procedure is described in U.K. Pat. No. 2,100,732 (1985) which further describes the reaction as carried out over a catalyst of a compound of metals of Group IV, zinc or tantalum. While the conditions are said to be particularly suitable when using primary or secondary amines or compounds such as alkylenediamines, no mention is made of amines which contain acetal groups. Although yields as high as 80% were reported, the Michael adduct was still formed.
U.S. Pat. No. 4,549,017 to MacIntyre et al.. (1985) discloses a process for making N-substituted acrylamides by reacting an acrylate ester with an amine over an alkyl metal oxide or alkoxide. The advance described is in the use of a drying agent to completely remove water from the feedstocks. It is stated that by avoiding water, the Michael reaction can be reduced.
U.S. Pat. No. 4,644,083 to Dahmen et al., (1987) discloses that polyvalent alcohols, such as ethylene glycol or glycerin, can be added to unsubstituted .alpha.,.beta.-unsaturated carboxylic acid amides, such as acrylamide, using base catalysis and the product is transamidated with a primary or secondary amine in the presence of catalytic amounts of carboxylic acid. The N-substituted-.beta.-saturated propionamides are then decomposed pyrolytically to N-substituted .alpha.,.beta.-unsaturated carboxylic acid amides. But there is no disclosure of using amines containing acetal groups and, in fact, the acidic transamidation described would decompose such acetal groups.
As can be seen from the above discussed references, a temporary protection of a double bond in an activated olefin by Michael addition of an alcohol is a known method of preventing undesired reactions at the double bond while the resulting adduct is subjected to other reaction conditions. This type of protection has been used to block the double bond in acrylic esters during aminolysis of the ester, to form the 3-alkoxy propionamide. Since Michael addition of either alcohols or amines to olefins is reversible under addition conditions, controlled conditions to avoid premature loss of protection or deblocking is critical. When the olefin is blocked with an alcohol, the addition reaction can be driven to greater than 99% completion by the use of excess alcohol. An excess of alcohol, therefore, might be expected to prevent loss of the alcohol blocking group. Johnson, J. Org. Chem., 51, 883-837 (1986) discloses that amines react with .alpha.,.beta.-unsaturated ketones, esters, amides and sulfones in the synthesis of substituted acrylamides and that the reaction is reversible. Kinetics are reported on the reaction in methanol.